In a video display device, an enhancement function for improving image quality of a displayed video is known. In a case where the enhancement function is executed, generally, when a maximum value of a tone is detected for each frame of a video signal and the level of the maximum value is low, gain is applied to a video signal in a part with a high tone for emphasis. In addition, when a minimum value of atone of a video signal is detected and the minimum value is high, compression gain is applied to a video signal in a part with a low tone to lower the tone. Such an enhancement function is used, so that a signal range of a video signal is broadened and contrast feeling of a displayed image is increased, thus improving image quality.
For example, Patent Document 1 discloses a liquid crystal display device automatically controlling contrast so that, along with the adjustment of luminance of a backlight, brightness/darkness of an image also comes close to the state before the adjustment. In this liquid crystal display device, an operator turns on/off a light source of a backlight device, thereby allowing to change luminance of an image and aim for power saving, an enhancement function works when the luminance is changed, contrast of a displayed image is controlled to be suited to the luminance, and even though the luminance of the backlight device is lowered, it is possible to obtain almost same level of brightness/darkness of the image as before the luminance is lowered.